“This year’s Living Planet Report is filled with ground-breaking figures, with most of the indicators describing a tremendous decline in ecosystem health. The calculation of the Living Planet Index shows an average 69% decline in population sizes of monitored mammals, birds, amphibians, reptiles and fish since the year 1970. Just as the R-number in epidemiology describes a virus’s ability to spread, and gross domestic product (GDP) reflects a country’s economic growth or decline, the Living Planet Index is a multifaceted metric that indicates the state of biodiversity on our planet. This metric is calculated by compiling extensive datasets on animal population sizes from all over the globe – and it reveals that populations, on average, are less than one-third of the size they were in 1970. Here, we tell the story behind the development and results of the Living Planet Index and dive deeper into the features of this unique biodiversity indicator.